The invention relates generally to semiconductor devices and integrated circuit fabrication and, in particular, to chip structures and fabrication methods for forming such chip structures.
Modern electronics achieve high levels of functionality in small and compact form factors by integrating multiple functions onto a single chip. A common fabrication process that allows high levels of integration at a relatively low cost is complementary metal-oxide-semiconductor (CMOS). CMOS processes build a combination of p-channel and n-channel metal-oxide-semiconductor field-effect transistors (MOSFETs) to implement logic gates and other types of digital circuits, as well as analog circuits.
A field-effect transistor includes a gate structure acting as a control electrode and spaced-apart source and drain regions between which a current can flow. A control voltage applied to a gate electrode of the gate structure controls the flow of current through a channel within the substrate between the source and drain regions.
Epitaxial semiconductor films may be used to modify the performance of field-effect transistors. For example, an epitaxial semiconductor film can be used to increase the carrier mobility through the channel of a field-effect transistor by inducing stresses in the channel. In a p-channel field-effect transistor, hole mobility can be enhanced by applying a compressive stress to the channel. One way in which the compressive stress can be applied is by embedding an epitaxial semiconductor material, such as silicon-germanium, at the ends of the channel. Similarly, electron mobility can be enhanced in an n-channel field-effect transistor by applying a tensile longitudinal stress to the channel. One way in which the tensile stress can be applied is by embedding an embedding an epitaxial semiconductor material, such as silicon doped with carbon, at the ends of the channel. The embedded stressors may operate as source and drain regions of the field effect transistor.
Improved chip structures and fabrication methods for forming such chip structures are needed.